Transversely reciprocating fluidized bed development method



Dec 16 1969 K. J. SWYLER 3,484,265

TRANSVERSELY RECIPROCATING FLUIDIZEI) BED DEVELOPMENT METHOD Original Filed July 21, 1966 2 Sheets-Sheet l INVENTOR. KARL J. SWYLER A TTORNE Y K. J. SWYLER Dec. 16, 1969 TRANSVERSELY RECIPROCATING FLUIDIZED BED DEVELOPMENT METHOD Original Filed July 21, 1966 2 Sheets-Sheet 2 E Y ww N S IU. L R A K United States Patent 3,484,265 TRANSVERSELY RECIPROCATING FLUIDIZED BED DEVELOPMENT METHOD Karl J. Swyler, Webster, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Original application July 21, 1966, Ser. No. 566,842, now Patent No. 3,380,437, dated Apr. 30, 1968. Divided and this application Oct. 9, 1967, Ser. No. 684,087

Int. Cl. B05b 5/00 US. Cl. 11717.5 1 Claim ABSTRACT OF THE DISCLOSURE This application is a divisional application of Serial No. 566,842 now US. Patent No. 3,380,437 filed July 21, 1966 in the name of Karl]. Swyler.

This invention relates in general to developing electrostatic images, and in particular relates to a method for developing electrostatic images by utilizing vibrational forces to fluidize a two-component developer material.

In the practice of xerography, as described in US. Patent No. 2,297,691, to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material affixed to a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the xerographic plate is electrostatically charged uniformly over its surface and then exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge in conformity with the configuration of the original light pattern.

The latent electrostatic image can then be developed by contacting it with a finely divided etlectrostatically attractable material such as a resinous powder. The powder is held in image areas by the electrostatic charges on the layer. Where the charge is greatest, the greatest amount of material is deposited; and where the charge is least, little or no material is deposited. Thus, a powder image is produced in conformity with the light image of the copy being reproduced. The powder is subsequently transferred to a sheet of paper or other surface and suitably affixed to thereby form a permanent print.

The electrostatically attractable developing material commonly used in xerography consists of a pigmented resinous powder referred to here as toner and a coarse granular material called carrier. The carrier is usually coated with a material removed in the triboelectric series from the toner so that a triboelectric charge is generated between the powder and the granular carrier. Such charge causes the powder to adhere to the carrier. The carrier also provides mechanical control so that the toner can be readily handled andbrought into contact with the exposed xerographic surface. The powder particles are then attracted to the electrostatic image to produce a visible powder image on the xerographic sur face.

A method of xerographic development of latent electrostatic images by fluidizing a two-component developer 3,484,265 Patented Dec. 16, 1969 Ice material in a development zone is described in US. patent application Ser. No. 566,847 copending herewith. As described in that case, a quantity of two-component developer material is vibrated beneath a latent electrostatic image. The vibrations are so rapid that they cause the developer material to suspend itself in a fluidized mass or bed. As an image bearing xerographic surface is .passed through the development zone, it is contacted by the fluidized or constantly moving developer and image areas of the xerographic surface are developed with the toner material in the developer.

The present invention constitutes a new xerographic development method adapted to carry out fluidized bed deve'opment as described above and incorporates advantageous features over other xerographic systems.

Earlier embodiments of fluidized bed development machinery, as described for example in the aforementioned patent application, had no provision for retoning carrier particles which became depleted of toner due to the toner deposition in image areas. The present invention,

on the other hand, takes advantage of the inherent low.

to continuously introduce freshly toned carrier particles.

into and out of the development zone. Due to the fluidized state of the developer in the development zone, the coefficient of friction between the deveoper and the tray,

is ,reduced. A slight tilt of the fluidized bed will thus result in a flowing action of the entire fluidized bed in the direction of tilt. By introducing a supply of freshly toned carrier to the high side of the titlted development zone and concurrently collecting the depleted developer as it flows past the lower part of the development zone, freshe 1y toned carrier can be supplied to the image areas. This characteristic of a fluidized bed of developer to flow is advantageous for use in xerographic machinery which require a continuous supply of developer such as automatic machinery.

Development electrodes are commonly used in xerography to provide solid area development. The electrode consists of a grounded or biased member positioned as. closely as possible to the xerographic surface to create an electric field in conjunction with the electrostatic image. Since development electrodes should be as close,

as possible to the xerographic surface it has been a continuous problem in automatic machines to provide an electrode that could be positioned close enough to the surface to create the electric field without interfering with developer flow. One approach to this problem has been to position an electrode plate or grid parallel to the xerographic surface and spaced therefrom. With such an approach, if the electrode is too distant from the xerographic surface, the effect is reduced and solid area capabilities are minimized. If, on the other hand, the electrode is too close to the xerographic surface, the developer which flows parallel to the image and electrode, is sus-v ceptible of jamming between the closely spaced electrode and xerographic surface.

The presence of a development electrode within the development zone adjacent the image bearing surface has another beneficial aspect. By simply constructing the electrode in the form of a wire network or the like, such Wire continuous developer flow and the high mass of the vibrator has already been described in U.S. Patent No. 3,393,- 663. The instant invention incorporates modified structures which solve the same problems but, simultaneously therewith solve the problem of striations and tracking found in the apparatus discussed in the aforementioned applications.

Striations are a fault of development systems wherein the developed image and final copy are characterized by underdeveloped strips across the image generally perpendicular or transverse to the movement of the image bearing surface. It is caused by an uneven contacting of the image bearing surface by the developer material. Striations occur in fluidized bed development systems which vibrate the developer material in the direction of the image movement. These striations are caused by the slapping effect that waves of fluidized developer have on the image bearing surface. These waves have crests in the direction of developer vibration, perpendicular to the movement of the image. As an image bearing surface is moved through the vibrating developer, it is rhythmically being slapped by these fluidized bed developer waves. This periodic slapping of the image bearing surface by the developer constitutes the uneven developer presentation to the image which causes the striations.

The reorientation of the reciprocations of the developer vibrating elements, in accordance with the present invention, eliminates those aforementioned transverse waves of developer. Since the reciprocation is across the movement of the image, developer Waves, if any are in fact formed, are not perpendicular to the direction of image movement. Consequently, the elimination of these transverse waves results in the elimination of their effect, viz, striations.

The problem of tracking is still encountered in conventional cascade development as well as other development systems. Tracking, or unwanted development streaks in the deposition of toner along the direction of movement of the image occurs when developer is caused to move in a constant linear path relative to the image. If one quantity of developer material includes a mass of undertoned carrier particles, or carrier particles which have been depleted of toner then that mass of carrier will be present along one line of the image bearing surface until it is replaced by properly toned carrier flowing through the development zone. Since the developer and image bearing surface move in a straight line relative to each other, the improperly developed image portion will be extended over one straight length of the image area.

In the apparatus of the instant invention, the vibratory elements are guided for reciprocation in a path transverse to the movement of the image. As such, the developer particles are constantly moving into and out of contact with the image as well as across the image surface in a compound movement. The movement of developer across the path of movement of the image is unique in the field of fluidized bed development. This movement dissipates the elTects of undertoned carrier by causing toned carrier to contact the image bearing surface at different sections across its path of movement through the development zone. As such, what would have formerly been a streak of underdeveloped image will now become developed since such line on the image will be contacted by masses of properly toned carrier on either side of the mass of undertoned carrier.

The transverse reciprocation of the developer also tends to eliminate tracking for another reason. As tWo ad.- jacent quantities of developer, one properly toned and the other undertoned, are reciprocated in contiguous relationship, the transverse agitation of the first quantity causes some of those developer particles to become intermixed with the adjacent second quantity at the interface of the two quantities. Conversely some of the undertoned carrier from the second quantity will be caused to move into the developer of the first quantity. This intermixing of the toned and undertoned carrier at similar interfaces across the extent of the development zone thus tends to spread out and reduce undertoned carrier quantities within the zone. This characteristic effect of the traversely reciprocating fluidized bed thus tends to minimize tracking by presenting uniformly toned carrier to all portions of the image.

The mounting of the vibratory elements for movement transverse to the movement of the image bearing surface also lends itself to a mechanical arrangement of the vibratory elements unique in the fluidized bed development art. The arrangement, as described herein, is mounted inde pendently of the main drum drive shaft as well as the other processing stations. Since the vibrational elements are independently mounted, their movement within the development station does not effect, by vibration, the movement within any other station of the sysem.

It is therefore an object of the present invention to develop latent electrostatic images.

It is a further object of this invention to improve fluidized bed development of xerographic images.

A further object of the invention is to eliminate tracking in the development of latent electrostatic images.

A further object of the invention is to eliminate striations in the development of latent electrostatic images.

These and other objects of this invention are obtained by applying a vibrational force to a two-component developer material in a direction transverse to the path of movement of a latent electrostatic image bearing surface and by applying the vibrational force so rapidly that the mass developer material will be suspended in a fluidized mass to contact and develop images on the surface.

For a better understanding of the invention, as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings wherein:

FIGURE 1 is an end sectional view of the developing apparatus constructed in accordance with the invention.

FIGURE 2 is a front view of the development apparatus as shown in FIGURE 1.

FIGURE 3 is a diagrammatic section view illustrating xerographic development apparatus adapted for continuous and automatic operation which embodies the development apparatus of the instant invention.

FIGURE 4 is an upper right perspective view of the vibrating elements as shown in FIGURE 3.

Essentially the apparatus of the invention illustrated in the described embodiments, includes a developer supporting plate positioned beneath at least a portion of a latent electrostatic image bearing drum and concentric therewith. Development electrode wires are positioned in the development zone between the plate and image bearing surface. Means are then provided to reciprocate the electrode wires and developer supporting plate beneath the rotating drum in a direction across the path of movement of the drum. When two-component developer is introduced between the plate and image, the vibratory motion imparted thereto by the wires and plate causes the vibrated developer to suspend itself in a fluidized mass or bed in contact with the image in the same manner as described in the above cited copending applications, Patents Nos. 3,380,437 and 3,393,663. The continued vibration imparted to the developer causes the individual particles to move into and out of contact with the imagebearing surface. The orientation of the vibration across the movement of the image-bearing surface imparts a compound motion to the developer within the development zone. As such, the developer not only moves along the direction of motion of the image due to its general mass flow but also moves transverse with respect thereto. This compound movement of the developer with respect to the image eliminates tracking and striations which might otherwise occur if the developer were vibrated in another direction.

The transfer of the toner particles from their associated carrier beads to image areas principally occurs during this contact period. The deposition of toner to image areas is physically caused either by the attraction of the image exceeding the attraction of the carrier for the toner or the toner being jarred loose from the carrier by the force of contact as it strikes the xerographic surface whereupon the change in the image areas attract the loose toner.

As the developer is suspended within the fluidized bed it has the appearance of a fluid with the entire bed of developer being of a substantially homogeneous density throughout. This uniform density across the length of the development zone insures the presentation of even quantities of developer to all portions of the image across the Xerographic surface. Consequently, the possibility of underdeveloped strips of image areas caused by the uneven presentation of developer to the image areas is minimized.

The developer composition may be of the conventional type as presently employed in commercial xerographic machines which use cascade techniques. Such as composition is defined, for example, in Walkup Patent 2,618,- 551. An example of such a composition comprises carrier beads of glass or steel covered with and encased in a suitable coating such as vinyl chloride which imparts the necessary triboelectric properties to the toner upon contact. The toner, usually a pigmented resinous material or the like which can be used to develop Xerographic images, may be blends or copolymers of styrene and n-butyl methacrylate, pigmented with about 10 percent carbon black. A typical carrier size is 30-50 mesh. A typical toner size is -10 microns.

In the illustrated embodiment of FIGURE 1, a latent electrostatic image is adapted to be formed on a xerographic surface shaped in the form of a drum 10. While a drum has been shown as readily adapted for use in this type of a system, it should be understood that any xerographic surface such as a plate or belt may be similarly employed. The drum shaped xerographic surface is mounted on a main drum drive shaft 12, for rotation in either direction. The motion of the drum acts to sequentially bring the various portions of the image bearing surface into the development zone 14, for development within the fluidized bed of developer.

Positioned immediately beneath a portion of the drum is an arcuate plate 16, shaped concentrically With the drum 10. The arcuate plate 16 is mounted adjacent opposite ends of the drum by rigid mounting plates 18. The lower portions of these mounting plates are attached to flexible metallic sheets 20, the lower ends of which are mounted to a base 22 by any suitable mounting mechanism. As shown herein brace bars 24 adjacent the interface of the flexible sheets 20, and base 22 provide the attachment.

Also positioned in the development zone between the drum, and arcuate plate 16, is a vibratory screen 26. The vibratory screen is also mounted arcuately and concen tric with both the drum and arcuate plate. The opposite ends of the screen as shown in FIGURE 2 are mounted into the mounting plates 18, of the vibrational elements through any suitable insulating barrier 28, as of polyurethane foam or the like. The screen is adapted to be grounded or receive an electrical bias by a potential source 30. Such electrical connection is adapted to render the screen a development electrode for the establishment of an electric field adjacent the image.

Motion to the vibrational elements is imparted by any suitable motor means. The apparatus as disclosed in this embodiment for causing the vibration is a motor 32 mounted on a suitable table 34, in alignment with the mounting plate 18. A connecting rod 36, is formed with apertured ends 38, 40. The first aperture end 38, is pivotally connected to the rotating circular drive plate 42, of the motor 32 off center from the axis of the plate to thereby cause an oscillation of the connecting rod 26. The opposite end 40, of the connecting rod 36, is pivotally attached to the adjacent mounting plate 18, of the vibrating elements. As such upon rotation of the motor 32, and circular drive plate 42, the vibrating elements will be oscillated toward and away from the motor 32, in a direction transverse with respect to the movement of the image bearing surface.

When such motion is imparted to the vibratory elements with two-component developer in the development zone 14 above the arcuate plate 16, the vibrations imparted to the developer by the screen 26 as well as the plate 16 will cause the developer to rise, suspending itself in a fluidized mass or bed throughout the space of the development zone 14 between the arcuate plate 16, and the image bearing surface of the drum 10. The motion of the screen 26, which is concurrent with the motion of the arcuate plate 16, by virtue of their common connection through the mounting plates 18, provides the majority of vibration for fluidizing the developer. Furthermore, when the potential is applied to the screen to cause a development electrode eflect, solid area capabilities are obtained and readily controlled.

In order to achieve a mass flow of developer through the development zone 14, a developer supply hopper 44 is positioned to one side of the arcuate plate. The hopper is provided with front, back and side walls 46 and an open top surface 48 for the addition of more developer. The lower face 50 thereof is inclined in a direction towards the development zone 14 for gravity feed of the developer. Positioned adjacent the outlet orifice 52 of the hopper are flexible hose-like connecting elements 5'4, connecting the hopper 44 with an intermediate chute 56 which is secured to the arcuate plate 1.6. The hopper 44, flexible connecting elements 54 and chute 56 extend the entire length of the development zone for gravity feeding developer along the entrance portion of the development zone. By this simple arrangement additional developer may be poured through the development zone to replace the developer which becomes depleted of toner as toner is depleted to the image through development.

To collect the toner-depleted developer as it flows beyond the development zone, any suitable bucket means 58 or the like may be positioned adjacent the development zone 14 on the side thereof remote from the hopper 44 and input chute 56. As the developer in the development zone is forced from the development zone by the introduction of freshly toned developer, the depleted developer is being continually forced from the development zone and gravity dropped into the collector bucket.

The effect of the mass flow of developer along the direction of the image movement in combination with the reciprocation of the vibration imparting elements transverse with respect to the mass flow, imparts a compound motion to the developer as it moves through the development zone. As discussed above, this compound motion of developer along the path of image movement, as Well as transverse with respect thereto, eliminates striations and tracking in the developed image which have been prevalent in many forms of development systems.

In operation, a latent electrostatic image is first formed on the drum 10. The drum is then set in motion by any conventional power source not shown. Concurrent with the movement of the drum, the vibration imparting elements are set in motion by activation of the motor 32. This is done with a supply of two-component developer in the hopper which will be gravity fed through the development zone. At the same time, the screen 26 is given an electrical bias to thereby produce a development electrode field adjacent the image bearing surface. The vibrations of the arcuate plate 16 and screen 26 thus cause developer thereabove to fluidize itself for contacting and developing the image on the drum. After one or plural passes of the drum through the development zone 14, motions of the drum and vibrational elements may be stopped since development has been accomplished.

Shown in FIGS. 3 and 4 is xerographic apparatus embodying the present invention constructed for continuous and automatic operation. The elements of this machine are all conventional in the xerographic art with the exception of the development station which forms the basis of the present invention. For the purpose of the present disclosure, the several xerographic processing stations in the path of movement of the xerographic surface may be briefly described as follows:

A charging station A, at which a uniform electrostatic charge is deposited on the photoconductive layer of the xerographic drum;

An exposure station B, at which the light or radiation pattern of copy to be reproduced is projected onto the drum surface to dissipate the drum charge in the exposed areas thereof to thereby leave a latent electrostatic image of copy to be reproduced;

A developing station C, which forms the basis of the present invention, at which a xerographic developing material, including toner particles having an electrostatic charge opposite to that of the electrostatic latent image, are moved into contact with the drum surface, whereby the toner particles adhere to the electrostatic latent image to form a xerographic powdered image in the configuration of the copy being reproduced;

A transfer station D, at which the xerographic powder image is electrostatically transferred from the drum surface to a transfer material or a support surface; and,

A drum cleaning and discharge station E, at which the drum surface is brushed to remove residual toner particles remaining thereon after image transfer, and at which the drum surface is exposed to a relatively bright light source to effect substantially complete discharge of any residual electrostatic charge remaining thereon.

The xerographic development apparaatus illustrated in the embodiment of FIGURES 3 and 4, is constructed of two major sections, a developer vibrating assembly 62, and a developer recirculation assembly 64. The purpose of the developer vibrating assembly is to impart the vibratory motion to two-component developer adjacent the latent electrostatic image bearing surface. The purpose of the developer recirculation assembly is to move developer to the input end of the developer vibrating assembly after it has been moved beyond the developer vibrating elements.

The developer vibrating elements as shown in FIG- URES 3 and 4 are quite similar to those shown in the first embodiment. The arcuate plate 116, is positioned concentric with the drum in an area vertically offset from the vertical center line of the drum 10, to facilitate rapid movement of developer through the development zone 14. The opposite ends of the arcuate plate 116 are secured by suitable means to mounting plate 118 positioned adjacent the opposite end faces of the drum. The mounting plates are provided at each end with suitable guide pins 66, three for example, for mounting through aligned apertures 68 is guide plates 70. The cooperation of the guide pins 66 and apertures 68 restrains the arcuate plate 116 and the rest of the vibratory elements for motion in a purely reciprocatory longitudinal path.

In the same manner as described in the first embodiment a suitable screen 126 is secured concentric with and between the drum and arcuate plate 116 for aiding in vibrating the developer material. The screen is grounded or provided with a bias from any suitable source of potential 30 to thus create an electric field adjacent the image. To allow a bias to be placed on the screen 126 but not the plate 116 the screen is mounted in the end plates 118 through suitable insulating barriers 128 as of polyurethane foam or the like as described in the first embodiment.

In order to guide the vibrated developer in a return path towards the developer recirculation assembly 64, a plate 72 with a J-shaped cross-section is also secured at its opposite ends between the mounting plates 118. The plate 72 is thus vibrated with the arcuate plate 116 and screen 126 during operation for maintaining the developer in a fluidized state. The developer thus exhibits a movement 8 down the longer leg 74 of the plate 72 towards the developer recirculation assembly 64 after reversing direction at the curved portion 76.

The developer recirculation assembly 64 is similar to the conventional type employed in most cascade development units. In the lower portion of this housing a developer sump 78 is provided containing a supply of twocomponent developer for feeding into the development zone 14. A bucket conveyor assembly comprising a plurality of buckets 80 mounted on a flexible endless belt 82 is held in position by two rollers 84 and 86. One of these rollers 84, is connected to a suitable power source, not shown, for moving the buckets in the direction of the arrows as shown in FIGURE 3. The buckets act to raise the developer from the sump 78 to an elevated position for gravity feed to the development zone 14. The entire system is enclosed and has adjacent one side there a toner dispenser for adding toner to the system to thereby replace toner which has been depleted due to development of images.

AlsO within the developer recirculating assembly are an upper and lower plate 92, 94 spanning the distance across the developer recirculating assembly 64. This distance is the equivalent of the length of the drum 10. These plates act as a developer input chute 96, for the introduction of developer into the space between the arcuate plate 116 and drum 10. This chute 96 is fixed with respect to the developer recirculating assembly and does not vibrate with the other vibratory elements of the machine.

To insure that the entire development system is closed in the areas between the developer recirculating assembly 64 and the developer vibrating assembly 62, flexible connecting elements 98 are employed to span the distance between these two assemblies. As shown in FIG- URES 3 and 4 this flexible connecting assembly comprises a series of, four for example, flexible sheets. A gum rubber film or the like may be readily employed. A first flexible sheet is connected above the space between these two assemblies and may be connected by any adhesive material with a bracing member, as backing bar 102, to insure a non-porous connection. A supplemental bar 104 secured between the mounting plates may hold the vibratory end of this sheet. Similar sheets may be employed on the opposite sides of the connection and a fourth sheet may span the lower portion of the juncture. As such, the developer recirculating assembly 64, the developer vibrating assembly 62, the portion of the drum 10 being developed and the flexible connecting elements 98 define a closed development system.

Motion to the developer vibrating assembly may be accomplished by a motor 132 similar to that employed in the embodiment of FIGURES 1 and 2. The motor 132 is adapted to be positioned adjacent one of the vibratory mounting plates 118. A connecting rod 136 with apertured ends similar to that employed and shown in FIG- URE 2 is positioned for the connecting mounting plate 118 to the rotating circular plate 142 of the motor. The end of the connecting rod which is pivotally mounted to the motor is offset slightly with respect to the center of the circular plate of the motor to thereby convert the rotation of the drive plate to a reciprocation of the vibrating elements.

To operate the development apparatus of the embodiment of FIGURES 3 and 4 it is first necessary to activate the various processing stations outlined above. Such activation may be done by a general cycle initiating means similar to that used in any of the known continuous and automatic xerographic machines. Such general cycle initiating means will activate all operative stations including the drum driving means, developer conveying apparatus and the vibrating instrumentalities in the development zone in addition to initiating the bias on the screen.

As the image bearing surface passes the development zone the developer conveyor is continually bringing the two-component developer into the input chute for gravity feeding developer to the development zone above the arcuate plate. As the developer contacts the arcuate plate and electrode screen, the continuous vibrations encountered reciprocate the developer between the arcuate plate and image bearing surface.

The ground or bias on the vibrating electrode screen establishes an electric field adjacent the image. In addition to creating the field, the vibrations of the screen assist in fluidizing the developer contacted thereby. The screen, as mentioned above, is of such mesh as to allow the vibrated developer particles to freely move between the arcuate plate and image bearing surface without interference from the screen.

As the fluidized cloud of developer flows past the arcuate plate and image it contacts the vibrating arcuate portion of the J-shaped plate. Here the direction of the entire fluidized bed of developer reversed. The fluidized bed continues to move in this reverse direction back towards the sump. It is noted that longer leg portion of the J-shaped plate is tilted in the desired direction of flow to facilitate the developer return to the sump. As the developer passes the final portion of the J-shaped plate it moves into contact with the sump area of the developer recirculating assembly. Since this portion of the system is not in vibration, the fluidized bed is dissipated and the developer resettles in the sump for subsequent recycling through the development zone.

While the present invention as to its object and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby; but it is intended to cover the invention broadly within the spirit and scope of the appended claim.

What is claimed is:

1. A method of developing latent electrostatic images on an image-bearing member mounted for movement through a development zone including the steps of providing a supporting plate in the development zone beneath and spaced from at least a portion of the image-bearing member to be developed,

flowing a quantity of two-component developer material including carrier particles and an electrostatically attractable powder across the supporting plate and through the development zone,

moving the image-bearing member through the development zone substantially parallel to the movement of the flowing developer to present sequential sections of the image-bearing member for its development,

providing a developer vibrating member in the development zone in the path of flow of the developer material and reciprocating said developer vibrating member through the flowing developer material in a direction of movement substantially transverse to the movement of the flowing developer material, said reciprocations being sufficient to impart lateral motion to the flowing developer material and to fluidize the developer material into image developing contact with the image-bearing member.

References Cited UNITED STATES PATENTS 2,759,450 8/1956 Vyverberg 117-17.5 X 3,008,826 11/1961 Mott et al. 117-17.5 X 3,013,890 12/1961 Bixby l18637 X 3,108,894 10/1963 Stowell 117--17.5 3,254,625 6/1966 Armstrong 118-429 X 3,257,223 6/1966 King 117-17.5 3,263,234 7/1966 Epstein et al. 11717.5 X 3,349,750 10/1967 Donalies 118-637 FOREIGN PATENTS 848,733 9/ 1960 Great Britain. 889,951 2/1962 Great Britain.

WILLIAM D. MARTIN, Primary Examiner EDWARD J. CABIC, Assistant Examiner US. Cl. X.R. 118-637 

